FIG. 5 is a sectional view illustrating a work clamp of a conventional wire bonding apparatus. This work clamp has a mechanism of preventing oxidation of copper if an object of bonding is a bare copper lead frame or if a bonding wire is copper. This mechanism introduces an inert gas such as nitrogen gas into an opening 17 leading to a bonding area.
A semiconductor device in a form of a lead frame 12 holding a die 18 is arranged on a platform or an upper plate 29 of a wire bonding apparatus. The upper plate 29 has a heating mechanism for raising a temperature of the lead frame 12. A wind clamp 16 fixes the lead frame 12 onto the upper plate 29. The opening 17 of the wind clamp 16 is arranged on the lead frame 12 so as to provide an access to the bonding area by a wire bonding work. That is, the bonding area including the die 18 and a part of the lead frame 12 is exposed by the opening 17.
The wind clamp 16 has a cavity 22 connected to the opening 17. A cover 20 is arranged on an upper face of the wind clamp 16 and covers the cavity 22 so as to limit exposure of the cavity to the air containing oxygen. Further, the wind clamp 16 has a conduit 24 therein for switching a direction of nitrogen gas toward the cavity 22. The conduit 24 is arranged so that the nitrogen gas passes through the cavity 22 and then, is fed to the opening 17. The nitrogen gas is introduced from a gas inlet 26 of the wind clamp 16. The gas inlet 26, the cavity 22, and the opening 17 communicate with each other. In this structure, in order to reduce a pressure of the nitrogen gas introduced from the cavity 22 into the opening 17 as compared with a pressure of the nitrogen gas introduced from the conduit 24 into the cavity 22, the cavity 22 has a sectional area larger than that of the conduit 24.
On a bottom face of the wind clamp 16 between the wind clamp 16 and the upper plate 29 or the platform, a hollow space 28 is also provided. The space 28 plays a role of receiving the nitrogen gas from the gas inlet 26 and having the nitrogen gas passed toward the cavity 22 through the conduit 24. Moreover, the space 28 distributes the nitrogen gas to the lead frame 12 in order to protect the lead frame 12 from oxidation. At an end portion of the space 28 far from the bonding area 17, the air directly communicates with the space 28 (See Patent Document 1, for example).
Patent Document 1: US2005/0161488 (FIG. 4)